In the past, low density closed cell polyethylene foam, (a non-crosslinked polymer of ethylene) has been extensively used in the packaging industry as a cushioning material or as dunnage, but it has not been fully utilised as a lagging or wrapping material on account of its low shear strength. This material is ideally suited as a protective lagging material as it is totally inert, it is soft and does not scratch and it provides non-slip contact with other surfaces. For example, packaging materials having these properties are used to provide a protective lagging for high quality injection mouldings in plastics material, and electronic equipment including computer hardware, but may also be used as a general purpose packaging material for a wide range of products having a high quality finish including furniture. Corrugated paper or cardboard has been used for this purpose but suffers from many disadvantages. For example, corrugated cardboard is water-absorbent which may cause the material to disintegrate when damp, and the adhesives used to adhere the paper laminae together can cause staining. Furthermore, equivalent laminated plastics materials are currently significantly cheaper to produce than laminated paper materials.
It has been found that the strength of low-density plastics foam materials in thin film form can be greatly increased by adhering this material to a stronger high density plastics film material with the added advantage that air may be entrapped between laminae of the two different materials thus increasing its cushioning properties. For example, high density polyethylene film may be adhered to a film of low density closed cell polyethylene foam to provide a composite laminate material, preferably formed with a single layer of each material and with a certain amount of air entrapped therebetween.
The difference in density and/or composition between the two films to be laminated results in a difference in tackifying temperatures, and melting point temperatures. Thus it is difficult to achieve complete molecular fusion when heat is applied, which may be undesirable in any case as heat shrinkage and local thinning of the laminate would occur. Suitable polymeric adhesive may be used to effect a strong bond between the films but this increases costs and causes other problems in the manufacture of plastics laminates known to those in the art.